yield compared to SHF, and energy recovery of the process was improved due to
use of immobilized yeast cells. Regenerated beads exhibited fermentation efficiency
of 79.8% for four cycles. The treatment of algal biomass with CaO before the
process of hydrolysis can also help in giving overall increase in reducing sugar
yield (Khan et al. 2017). In one of the studies, utilization of mixed microalgae
culture has been reported for bioethanol production. The effects of different pretreatment strategies (acidic, alkaline, and enzymatic) were also studied, and it was
reported that dilute sulfuric acid with MgSO 4 gave higher yield of reducing sugars
as compared to only dilute sulfuric acid. Among all the processes employed,
enzymatic process was reported to give the highest yield of reducing sugars
(Shokrkar et al. 2017). The analysis of literature reveals that many approaches are
available to optimize the process and maximize the ethanol yield with better utilization of the resources. A well designed approach with optimization studies for
specific system need to be developed to facilitate the commercial scale application.
There is also a possible solution of genetic modification in the microalgae which
can induce the direct production of ethanol from lifecycle of microalgae. The
functional genetic diversity of microalgae is very large and can be utilized in
developing specialized strains to directly produce bioethanol. The activity of
pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) enzymes in the
microalgae needs to be increased which will convert the fixed carbon into bioethanol. To modify the microalgae genetically, it will require more focused research
and time. Currently, genetic modifications have made possible to increase the
carbohydrate accumulation in microalgae (Silva and Bertucco 2016), and hence it
definitely offers as a possibility even for direct ethanol production.
5.3 Biogas
Biogas production is an anaerobic process in which a gas is generated by decomposition of organic materials with the help of specialized organisms. Biogas mainly
consists of methane (55–75%) and carbon dioxide (25–45%) with other constituents
like H 2 , N 2 , water vapor, and H 2 S in minor fractions. The production process
consists of stages like hydrolysis, acidogenesis, acetogenesis, and methanogenesis.
Microalgae can also be a potential feedstock for biogas production, more promising
than the utilization in other forms of biofuels due to the energy efficiency of the
process for biogas. There is no requirement of lipid extraction process and the
product, that is, biogas obtained in gaseous form does not require any separation.
All the macromolecules present in the microalgae are typically utilized for the
biogas fermentation process. The raw microalgae as well as the residuals from the
4 Process Intensification of Biofuel Production …
73
use of immobilized yeast cells. Regenerated beads exhibited fermentation efficiency
of 79.8% for four cycles. The treatment of algal biomass with CaO before the
process of hydrolysis can also help in giving overall increase in reducing sugar
yield (Khan et al. 2017). In one of the studies, utilization of mixed microalgae
culture has been reported for bioethanol production. The effects of different pretreatment strategies (acidic, alkaline, and enzymatic) were also studied, and it was
reported that dilute sulfuric acid with MgSO 4 gave higher yield of reducing sugars
as compared to only dilute sulfuric acid. Among all the processes employed,
enzymatic process was reported to give the highest yield of reducing sugars
(Shokrkar et al. 2017). The analysis of literature reveals that many approaches are
available to optimize the process and maximize the ethanol yield with better utilization of the resources. A well designed approach with optimization studies for
specific system need to be developed to facilitate the commercial scale application.
There is also a possible solution of genetic modification in the microalgae which
can induce the direct production of ethanol from lifecycle of microalgae. The
functional genetic diversity of microalgae is very large and can be utilized in
developing specialized strains to directly produce bioethanol. The activity of
pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) enzymes in the
microalgae needs to be increased which will convert the fixed carbon into bioethanol. To modify the microalgae genetically, it will require more focused research
and time. Currently, genetic modifications have made possible to increase the
carbohydrate accumulation in microalgae (Silva and Bertucco 2016), and hence it
definitely offers as a possibility even for direct ethanol production.
5.3 Biogas
Biogas production is an anaerobic process in which a gas is generated by decomposition of organic materials with the help of specialized organisms. Biogas mainly
consists of methane (55–75%) and carbon dioxide (25–45%) with other constituents
like H 2 , N 2 , water vapor, and H 2 S in minor fractions. The production process
consists of stages like hydrolysis, acidogenesis, acetogenesis, and methanogenesis.
Microalgae can also be a potential feedstock for biogas production, more promising
than the utilization in other forms of biofuels due to the energy efficiency of the
process for biogas. There is no requirement of lipid extraction process and the
product, that is, biogas obtained in gaseous form does not require any separation.
All the macromolecules present in the microalgae are typically utilized for the
biogas fermentation process. The raw microalgae as well as the residuals from the
4 Process Intensification of Biofuel Production …
73